Comparison of serum creatine kinase and creatine kinase MB activities post marathon race versus post myocardial infarction.

Serial total creatine kinase (CK) and CK MB activities were determined in the serum of seven runners following a marathon race and compared to enzyme activities in the sera from five patients following acute myocardial infarction (AMI). In the runner's sera, total CK and CK MB activities were significantly elevated at 1, 24, 48 and 72 hours post marathon race when compared to the 1 hour pre-marathon samples (p less than 0.01). Serum CK MB activities peaked at 24 hours in both groups of subjects. The MB activities 24 hours following the marathon were substantially higher (91 +/- 30 U/l; mean +/- SD) than the MB activities 24 hours following AMI (46 +/- 38 U/l). However, the percentages of CK MB 24 hours following the marathon and AMI were almost identical (7.0 +/- 2.4% and 7.2 +/- 2.3%, respectively). Furthermore, CK and CK MB clearances were significantly prolonged (p less than 0.02 and p less than 0.001, respectively) following the marathon race (T 1/2 CK, 49 hours; T 1/2 CK MB, 29 hours) as compared to following AMI (T 1/2 CK, 27 hours; T 1/2 CK MB, 12 hours). These results suggest release of CK MB from the skeletal muscle of marathon runners. Therefore, we recommend that elevation of CK MB in the range indicative of myocardial damage be interpreted with caution in long-distance runners.